The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
There are generally two types of media used in bit patterned recording (BPR). A first BPR media type includes bit islands that are arranged around a track in a uniform manner. In other words, there is no difference between data islands (i.e., bit islands in data field) and servo islands (i.e., bit islands in servo field) and the spacing between the data islands and the servo islands is the same. The frequency and phase of a data clock is the same as the servo clock.
A second BPR media type includes bit islands that are not positioned around the track in a uniform manner. In other words, the data islands and the servo islands are printed with different spacing. Typically the servo islands are printed farther apart than the data islands to provide additional protection against distortions such as inter-symbol-interference (ISI) when reading the servo islands. The frequency and phase of the data clock are different than the servo clock.
Synchronization of the data clock when using the first BPR media type is relatively straightforward since the servo field may be used to directly adjust the phase of the data clock. The servo field for the first BPR media type is typically written at the factory to provide a repeatable reference from which an error between the data clock and the data islands can be determined. Bit positioning accuracy requirements for the second BPR media type are more stringent than those for the first BPR media type because the frequency and phase of the data clock are different than the servo clock.
Referring now to FIG. 1, phase misalignment of the data clock and the data islands on the second BPR media type is shown. If the phase of the data clock is misaligned as shown, writing instants will not coincide with positions of the data islands. As a result, the user data will not be recorded properly to the second BPR media type. The writing errors can be difficult to detect and/or correct. In FIG. 2, proper alignment of the data clock and the data islands is shown.